Non-invasive breath tests can serve as valuable diagnostic tools in medicine as they can determine particular enzymatic and metabolic functions in vivo. This has wide applications in the fields of gastroenterology, oncology, hepatology and nutrition control. A 13CO2 breath test measures increased levels of 13CO2 in exhaled breath after ingestion of a stable 13C isotope labelled substance and its subsequent metabolism with a specific function or enzyme as a rate limiting step. Breath samples are collected and analysed, for example, with a Kibion® infrared instrument, measuring the time between ingestion by the patient of the labelled substance and its appearance in the exhaled breath.
In the UK, the most common 13C substrates (except for 13C Urea, available commercially as Diabact) are available directly from Seahorse Laboratories as specials1:
In the UK, the most common 13C substrates (except for 13C Urea, available commercially as Diabact) are available directly from Seahorse Laboratories as specials1:
| Substrate | Metabolic Indication |
| 13C Methacetin | Liver function |
| 13C Sodium Acetate | Gastric emptying (liquid) |
| 13C Octanoic Acid | Gastric emptying (solid) |
| 13C Mixed Triglyceride | Pancreatic function |
1Unlicensed medicinal products for human use (commonly described as “specials”) which have been specially manufactured or imported to the order of a doctor, dentist, nurse independent prescriber, pharmacist independent prescriber or supplementary prescriber for the treatment of individual patients.